The question of whether a controversial California law that would ban gay "conversion therapy" violates the First Amendment right to free speech heads to a San Francisco appeals court today.

The bill, which bans efforts by therapists to change the sexual orientation of gay and lesbian young people, was signed into law last fall by California Gov. Jerry Brown. It was set to take effect at the start of 2013 but the 9th U.S. Circuit Court of Appeals put it on hold pending resolution of court cases about the law's constitutionality. The bill, SB1172, "prohibit[s] a mental health provider ... from engaging in sexual orientation change efforts ... with a patient under 18 years of age."

The judges will consider whether the ban violates free speech and religious rights, and jeopardizes the livelihood of practicing therapists and counselors. Gay conversion therapy practitioners, a national association of Christian mental health counselors and the families of two teenage boys who say their sons benefited from the therapy brought the challenge to the law.

"The state has determined that the only permissible message [is that] same-sex attractions, behavior or identity are to be accepted, supported and understood, thus suppressing all other viewpoints to the detriment of licensed professionals and their vulnerable minor clients," attorneys for the group of challengers argue.

California was the first state to adopt such legislation, and the appeal is being watched closely around the country. Since the law passed, other states have been considering similar legislation that would ban gay conversion therapy.

James Guay, a licensed marriage and family therapist in Los Angeles, voluntarily tried to change his sexual orientation from age 12 until age 20. Guay, now 41, said as a 16-year-old he went to weekly conversion therapy sessions for a year with a licensed formerly gay Christian psychologist, and attended several conferences of people who said they were formerly gay.

Speaking to ABCNews.com from outside the 9th U.S. Circuit Court of Appeals today, Guay said that the state had an interest in protecting children from harm that he said could come from sexual orientation change efforts, or SOCE, by state licensed psychotherapists.

"It's psychological abuse that often takes years to recover from," he said. "Clients suffer from PTSD-like symptoms. ... All legitimate mental health and medical associations have come out against SOCE, saying it is ineffective and often harmful."

Guay said that even if the law remains in effect, parents would still be able to "shame" their kids for being LGBTQ (lesbian, gay, bisexual, transgender, queer/questioning), and nonlicensed religious counselors could still practice sexual orientation change efforts. He also pointed out that in January 2012 Alan Chambers, the current president of Exodus International, a Christian organization of former gays, admitted that 99 percent of people trying to change their sexual orientation couldn't.

"All legitimate mental health and medical associations have come out against SOCE, saying it is ineffective and often harmful," Guay said.

Matthew McReynolds of the Pacific Justice Institute, who argued against the law at Sacramento's Eastern District Court of California, told ABCNews.com that today's case was about First Amendment rights. McReynolds said that California was effectively telling therapists and counselors what they could and could not say.

"It's a free speech issue. ... The big debate over 'how far can the state go in the name of regulating the profession.' The state is seeking almost unlimited authority, so long as they call it professional regulation," he said.

McReynolds said the Pacific Justice Institute saw the challenge to the law as strictly a free speech issue, and not as a gay rights issue. He pointed out that California allowed minors to receive mental health treatment and therapy for virtually everything -- except for gay conversion therapy.

"They made this one exception. ... A lot of the debate has focused on young people supposedly being forced into this by their parents. But the legislation doesn't target that. It limits equally those who freely choose this kind of therapy," he said.

"It's very concerning to us that so many people are willing to ignore or overlook free speech concerns," he said, "when the issue involves gay issues and gay rights."